It's estimated that the average household brings in between 5 and 10 grocery bags full of groceries every week. Of that number at least one bagful ends up in the garbage each week as rubbish. This is a result mainly of fresh produce going off before it can be consumed, left overs that never get eaten and exotic ingredients that never get used.
The single biggest thing I have done to reduce waste is to menu plan. I menu plan weekly because that's about all my brain can manage and only buy fresh food as I need it. For example as I menu plan I write down exactly how many carrots I will need for the week based on what dishes I am cooking. If I only need 2 I buy 2 carrots and not a whole bag.
The other thing I do is write out the menu plan and store it in a plastic folder which I attach with magnets to the fridge. In this folder I put any new recipes I intend to try that week. Generally I have pulled these from magazines.
I now have almost no food wastage and the little I do have I feed to my worms.